Method and device for drilling to a predetermined surface

ABSTRACT

A method and a device for rock-drilling and/or earth boring of a number of drill-holes to a predetermined bottom surface are disclosed in which a reference surface defined by electromagnetic radiation is generated parallel to the bottom surface, the distance between the reference surface and the point at which drilling is to be initiated is measured in a direction common to all holes, the penetration of the drill-rod into the ground is added to said distance, and drilling is interrupted when the sum indicates that the bottom surface has been reached. The disclosed device comprises a reference surface finder for measuring the distance between the reference surface and the point at which drilling is to be initiated. The distance is measured by counting pulses generated by the finder. The penetration of the drill-rod into the ground is measured by counting pulses generated by a sensor coupled to the feed device of the rock-drilling machine.

United States Patent Lagerstrom [75] Inventor: Gunnar Lagerstrom, Ektorp,

Sweden {73} Assignee: Atlas Copco Aktiebolag, Nacka,

Sweden [22] Filed: May 2, 1974 [21] Appl. No.: 466,300

30 Foreign Application Priority Data May 15, 1973 Sweden 7306858 [52] US. Cl. 175/40; 33/1 I-I; 33/302; 73/151.5; 173/21; 299/1; 408/14; 408/16 [51] Int. Cl E2lb 47/04 [58] Field of Search 173/21; 175/40; 299/1; 73/151.5; 33/1 H, 302, 304; 408/10, 14, 16

[56] References Cited UNITED STATES PATENTS 3,491,624 l/l970 Poincenot 408/14 3,604,512 9/1971 Carter 299/1 FOREIGN PATENTS OR APPLICATIONS 2,005,479 3/1970 Germany 33/1 H June 24, 1975 Primary ExaminerFrank L. Abbott Assistant ExaminerWilliam F. Pate, III Attorney, Agent, or FirmFlynn & Frishauf 57] ABSTRACT A method and a device for rock-drilling and/or earth boring of a number of drill-holes to a predetermined bottom surface are disclosed in which a reference surface defined by electro-magnetic radiation is generated parallel to the bottom surface, the distance between the reference surface and the point at which drilling is to be initiated is measured in a direction common to all holes, the penetration of the drill-rod into the ground is added to said distance, and drilling is interrupted when the sum indicates that the bottom surface has been reached.

The disclosed device comprises a reference surface finder for measuring the distance between the reference surface and the point at which drilling is to be initiated. The distance is measured by counting pulses generated by the finder. The penetration of the drill-rod into the ground is measured by counting pulses generated by a sensor coupled to the feed device of the rock-drilling machine.

13 Claims, 5 Drawing Figures PATENTEDJUN 24 ms SHEET 1 METHOD AND DEVICE FOR DRILLING TO A PREDETERMINED SURFACE The present invention relates to a method and a device for rock-drilling and/or earth boring of a number of drill-holes to a predetermined preferably plane bottom surface. This bottom surface can e.g. be a surface which lies close to the surface of a road under construction. The invention is, however, not restricted to constructing roads but can advantageously be used in all those cases when drilling to a predetermined bottom surface is to occur.

BACKGROUND OF THE INVENTION The method presently used comprises a timeconsuming tracing out of each drill-hole in order to determine its required depth which furthermore must be indicated at the point where drilling is to occur. In order to reach the required depth a drill-rod which comprises one or more rod sections is used. In most cases drilling is to be interrupted when the last rod section only partly has penetrated into the ground. If drilling is not performed to the required depth protruding rock formations are left at the subsequent blasting. In order to remove these further drilling and blasting must be done. Before that the already blasted rock mass must be excavated. It is hereby a large risk that the buckets of the loading machines are damaged when they hit the protruding rock formations. In order to avoid these risks of damage and to avoid the timeconsuming work with post blasting and following further excavation it is essential that drilling is not interrupted until the required depth of the hole has been reached. In order to be sure about this it is common that the operator does not interrupt the drilling until the last rod section has been drilled entirely into the ground. This means unnessary drilling and blasting costs.

The object of the present invention is to achieve a simple and safe indication of how far the drilling work has advanced in relation to a reference surface defined by electro-magnetic radiation through which drilling can be interrupted when the predetermined bottom surface has been reached which according to an advantageous embodiment of the invention is done automatically.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is described below with reference to the accompanying drawings in which FIG. 1 shows an embodiment of the invention with freestanding reference surface finder.

FIG. 2 shows another embodiment in which the reference surface finder is mounted on the feed beam of the drilling aggregate.

FIG. 3 shows the embodiment according to FIG. 1 with a control system adapted thereto.

FIG. 4 shows the embodiment according to FIG. 1 with a simplified control system adapted thereto.

FIG. 5 shows the embodiment according to FIG. 2 with a control system adapted thereto.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS As shown in FIGS. 1 and 2 a reference surface 102 is produced by a rotating radiation source 101. This radiation source can e.g. consist of a laser made in the way shown in Swedish Pat. No. 347,351. The radiation source is directed such that the reference surface 102 is parallel to the predetermined bottom surface 103. For the drilling work a drilling aggregate is used, which comprises a chassis 104 on which a supporting arm 105 is mounted. A feed beam 106 for a rock-drilling machine 107 is mounted on the supporting arm. The rockdrilling machine is driven along the feed beam 106 by a feed motor 109 via a chain or a screw in a manner well known to a skilled person. a drillrod 108 is connected to the rock-drilling machine 107. In the embodiment according to FIG. 1 a freestanding reference surface finder is used which comprises a support 111, a telescopic mast 112, and an arm 113 for sensing the level of the point 99 on the ground 100 where drilling is to begin. The mast 112 is at its upper end provided with a photo detector 116 which comprises a number of photo cells e.g. such with the designation BPY63 manufactured by Siemens, which suitably are mounted such that the radiation source 101 can be sensed independent of its horizontal direction. The photo detector 116 is suitably provided with simple plastic optics for restriction of the vertical field of sensitivity and a filter which is adapted to the colour of the radiation source. Through this the influence of e.g. sun light is decreased.

The support 111 comprises reversible driving devices for the mast 112 and the arm 113. The mast can e.g be driven upwards through exposing its inner space to a fluid pressure and downwards by a pressure-fluid motor which via a wire fastened to the tip of the mast draws the mast together. The arm 113 can be driven by a reversible pressure-fluid motor or a reversible electric motor. In order to control the pressure-fluid supply electrically controlled valves are used which are supposed to comprise amplifiers or relays so that they can be driven by those signals which are achieved from logic circuits. Pulse generating sensors are connected to the drivings of the mast 112 and the arm 113. These can e.g. be made with rotating magnets which influence reed relays or so-called log-cell elements. The feeding of the drilling machine 107 is measured in a similar way. The arm 113 is movable between an upper limit position 114, which is situated at the same level as the lower limit position of the photo detector 116, and a lower limit position 115. The device according to FIG. 2 differs from the device according to FIG. I only thereby that the mast 122 is mounted on the feed beam 106. The mast 122 is driven by a motor 121.

With the designations used in FIG. 1 the following relation is achieved where A deisgnates the distance between the reference surface 102 and the bottom surface 103, H the distance between the limit position 114 and the reference surface 102, K the distance between the limit position 114 and the point of application 99, D the depth of the drillhole, and v the angle between the drilling direction and the vertical line.

With the designations used in FIG. 2 the following relation is achieved In this case H and K are measured in the drilling direction. K is here the constant distance between the lower limit position of the photo detector 116 and the pointof application 99.

The drilling machine 107 is in FIG. 3 shown with a, as a power supply disconnector operating, electrically controlled valve 47 which disconnects the pressurefluid supply through the conduit 48 to the hammer device of the drilling machine when a voltage, logic 1- signal, is supplied to the input 49. The valve 47 is supposed to comprise an amplifier through which control by means of logic signals is possible. The support 111 comprises a number of indicators or sensors 19, 21, 30, 31, and 32 and two pulse generating sensors 91 and 2, which is shown by means of the line 95. The indicator 19 produces a logic lsignal, also called signal, at its output when the arm 113 hits the ground. The indicator 21 produces a signal at its output when the mast 112 is in its highest position which if that should be wished can be adjustable. The indicator comprises the photo detector 116, amplifier with filter for surpressing undesirable signals and an output device e.g. a Schmitttrigger, which produces a signal at its output when the photo detector 116 senses the radiation source 101. The indicator 31 produces a signal at its output when the arm 113 is in its upper limit position 114. The indicator 32 produces a signal at its output when the photo detector 116 is in its lower limit position 114. The sensors 91 and 2 which are connected to the mast and arm motors have two outputs designated UP and DOWN. These sensors produce two phase shifted pulse trains so that the rotational direction of the sensors can be sensed. The sensors comprise pulse forming elements e.g. monostable vibrators and produce, therefore, logic l-pulses with constant duration either at output UP or at output DOWN depending on the rotational direction of the sensors. UP and DOWN designate and respectively according to practice and must, therefore, not be mixed with what is up and down in FIG. 1. A sensor 3 is connected to the motor 109 or the chain or screw driven thereby which sensor is of the same type as the sensors 91 and 2. This is shown by the line 97. An angle sensor 26 is connected to the feed beam 106 which is shown by the line 98. This sensor can either be made such that it gives a signal which is proportional to the angle v or such that it gives a signal which is porportional to cos v. The sensor can also be substituted by a thumbwheel switch. The feed beam 106 is provided with a drill guide 110 which comprises a pair of tongs .33, provided with an indicator, by which the drillrod 108 can be held. The indicator 33 produces a signal at its output when the tongs grip the drill-rod. The line 96 indicates the position of the indicator 33. Other electronics is mounted on the chassis 104 of the drilling aggregate. The control electronics is mainly built up from integrated circuits and shown as a logic circuit diagram. The control electronics comprises over already mentioned indicators and sensors three adders 4, 5, and 6. These are provided with two inputs and an output and work such that each pulse on each input produces a pulse at the output independent of their relative position in time. Furthermore, three UP/DOWN counters 7, 8, and 9 are incorporated. These are provided with a number of inputs and outputs of which only those which are used are shown. In order to simplify the description it is supposed that the counters react on logic l-pulses and produce logic l-pulses at their outputs. Input LOAD on counter 9 is an exception which is fed with logic O-pulses. The construction of the counters must be taken into account when using commercially available counters. This is most easily done by providing certain inputs and/or outputs with invertors. When a signal occurs at input CLEAR the counters are set to zero. Pulses which are supplied to input UP increase the value stored in the counter. Pulses supplied to input DOWN decrease the value stored in the counter. When the value becomes zero a signal is obtained at output BORROW. When a logic O-pulse is fed to input LOAD on counter 9 the value stored in counter 7 is transmitted to counter 9 which is indicated gy the arrow 45. The value stored in counter 7 is not influenced by this. The multiplier 11 multiplies the number of pulses coming from the drill length sensor 3 by the value cos v which either is achieved directly from the sensor 26 or, if the sensor 26 produces the angle value, is created in the multiplier 11. Three electro-mechanical impulse counters 12, 13, and 14 are incorporated in the system. These can of course be substituted by electronic count ers with digital displays. The counters l2 and 13 are provided with manual zero-setting 81 and 82 respectively. The counter 14 comprises two parallelly connected digital displays of which one is provided with manual preset 83. Pulses which arrive at input 43 count down the preset display and simultaneously count up the other digital display. when the preset display reaches the value zero a signal is obtained at output 44. The two digital displays are simultaneously restored by means of the draw magneto 80. The draw magneto 80 is supposed to comprise an amplifier through which driving by means of logic signals is possible. The pulse generator 24 continuously produces pulses the length and frequency of which are adapted to the counter 14. Two monostable vibrators 28 and 29 are incorporated in the system. These produce an output 1 a logic 1 pulse of predetermined length and at output 0 a logic O-pulse of the same length when the voltage at the input is changed from logic O-level to logic l-level. Seven SET/RESET flip-flops 10, 15, 16, 17, 18, 20, and 27 are incorporated in the system. These give lasting logic l-signal at output 1 and lasting logic O-signal at output 0 after having received a pulse at input S. When a pulse is supplied to input R the logic values of the output signals are reversed. The system furthermore comprises a number of AND-gates and OR-gates. An AND-gate, e.g gate 22, produces a logic l-signal at its output only if all inputs are supplied with logic l-signals. An OR- gate, e.g. gate 50, produces a logic l-signal at its output if one or mroe of the inputs are supplied with logic 1- signal. The gates may be provided with inverting inputs or outputs which is indicated by a small circle. Invertion means that a logic l-signal is changed to a logic 0- signal or vice versa. All electronic circuits in the system are provided with supply voltage from a voltage source, which may comprise an accumulator, via a holding relay 25. The voltage source and the relay are here supposed to be built together to one unit. The system comprises two contact devices 34 and 35 with momentary closing function. The conduits and 71 are connected to a voltage having logic l-level. Furthermore two indicators are incorporated which produce light and/or sound signals. These are shown as lamps 41 and 42.

The method according to the invention is realized in the following way. The radiation source 101 is directed such that the reference surface 102 becomes parallel to the bottom surface 103. The distance H K between the reference surface and the point of application 99 is measured by the mast 112 and the arm 113 and registered in the counter 14. To this the component Dcos v of the depth of the drill-hole is added. When the counter 14 indicates that the bottom surface 103 has been reached a signal is obtained at output 44. This signal shuts off the hammer device of the drilling machine 107 via the flip-flop 18, the gate 68 the output 40 of which is connected to input 49 on valve 47, and the valve 47.

In the following description of the function of the device according to FIG. 3 the designation high refers to a voltage having logic l-level and low to a' voltage having logic O-level. The initial condition for this description is that the voltage supply has been shut off and that the mast 112 and the arm 113 are not in anyone of their liinit positions. When pushing the contact device 34 voltage is supplied from the conduit 70 to the holding relay 25, through which all circuits are provided with supply voltage, and to input S of flip-flop 20. Through this its output l'becomes high through which output 0 of flip-flop 16 becomes high and the outputs of gates 61 and'62 low. Since the arm 113 is not in its upper limit position 114 the output of indicator 31 is low. Both inputs on gate 63 are therefore low and its output 37 therefore high. This output is connected to the motor of arm 113 such that the arm through this is returned towards the limit position 114. Since the photo detector 116 is not in its lower limit position 114 the output of indicator 32 is low. Since the output of indicator 31 is low the output of gate 66 is low and therefore both inputs on gate 65 low. Since the output of gate 61 is low both inputs on gate 64 are low. This means that the output 39 of the gate 64 is high. This output is connected to the driving of mast 112 such that the mast through this is returned towards the limit position 114. When the arm 113 reaches its upper limit position 114 the output of indicator 3] becomes high through which output 37 of gate 63 becomes low through which the driving of arm 113 is interrupted. When the mast 112 reaches the limit position 114 the output of indicator 32 becomes high through which output 39 of gate 64 becomes low through which the driving of mast 112 is interrupted. Since the outputs of indicators 31 and 32 both are high the output of gate 51 is high so that counter 7 is set to zero and output 1 of flip-flop 20 becomes low.

When the contact device 35 now is pushed voltage is supplied from conduit 71 to the monostable vibrator 28 through which this emits a logic l-pulse. This pulse restores via the draw magneto 80 the counter 14 so that its preset display shows the preset value corresponding to the distance A between the reference surface 102 and the bottom surface 103. The pulse furthermore sets counters 8 and 9 to zero, makes output 0 of flip-flop 18 high and its output 1 low, makes output 0 of flip-flop 17 high and its output 1 low, makes output 0 of flip-flop 16 low, makes output 1 of flip-flop low, and makes via gate 50 output 1 of flip-flop 27 low. If the preset display of counter 14 shows zero when the pulse is emitted from the monostable vibrator 28 output 44 is high and gate 67 therefore transmits the pulse to counter 12 which is used to register the number of drill-holes. Since outputs 1 of flip-flops 18 and 27 are low both inputs on gate 68 are low and its output 40 therefore low. This output is connected to input 49 on valve 47.

The hammer device of the drilling machine 107 starts and drilling can begin. Since the arm 113 is not in contact with the ground the output of indicator 19 is low and since output 0 of flip-flop 16 is low both inputs on gate 59 are low and therefore its output 36 high. This output is connected to the driving motor of arm 113 such that the arm through this is driven towards the ground. Since the photo detector 116 does not sense the radiation source 101 the output of indicator 30 is low. Since furtermore output 1 of flip-flop 27 is low both inputs on gate 57 are low and therefore its output low. Since furthermore output 0 of flip-flop 16 is low both inputs on gate 60 are low and therefore its output 38 high. This output is connected to the driving of mast 112 such that the mast through this is driven upwards. When the mast 112 is driven upwards and the arm 113 downwards thesensors 91 and 2 deliver pulses at output UP. These pulses are added by adder 4 which delivers them to input UP on counter 7. When the arm 113 reaches the ground the output of indicator 19 becomes high through which the driving of the arm is stopped via gate 59. When the photo detector 1 16 comes in contact with the reference surface 102 the output of indicator 30 becomes high through which the driving of mast 112 is interrupted via gates 57 and 60. Since the outputs of indicators 19 and 30 both are high the output of gate 22 is high. Through this output 1 of flip-flop 15 becomes high. As a result of this the monostable vibrator 29 delivers a logic 0-pulse to input LOAD on counter 9 through which the value stored in counter 7 is transferred to counter 9. Since output 1 on flip-flop 15 and output 0 on flip-flop 17 both are high pulses from the pulse generator 24 can pass through gate 23. These pulses are partly supplied to input DOWN on counter 9 and partly via the adder 6 to gate 56. Since output 0 on flip-flop 18 is high the pulses pass gate 56 and are registered in counter 14. During the drilling work the tongs of the drill guide 110 do not grip the drill-rod 108 so that the output of indicator 33 is low. When the drilling machine 107 is fed forwards along the feed beam 106 the sensor 3 delivers pulses at output DOWN. These pulses pass gate 53 since the output of indicator 33 is low. Since output 0 of flip-flop 10 is low and its output 1 is highthe pulses cannot reach counter 8 but are supplied :viagate 55 partly to counter 13 and partly to multiplier ll. Total drilling length is registered in counter 13. The incoming number of pulses from sensor 3 is multiplied by cos v in the multiplier 11 and the pulse number modified in this way is supplied to counter 14 via adder 6 and gate 56. The pulses from pulse generator 24 decrease the value stored in counter 9 until this becomes zero. When this occurs counter 9 delivers a pulseat output BORROW. This pulse is supplied to input S of flip-flop 17 through which its output 1 becomes high and its output 0 low. When output 0 of flip-flop 17 is low the pulses from pulse generator 24 cannot pass gate 23. Since output 1 of flip-flop 17 is high the outputs on gates 61 and 62 are low. Furthermore the output of indicator 31 is low so that output 37 of gate 63 is high. As a result of this the arm 113 is driven towards its upper limit position 114. Since the output of indicator 31 is low the output of gate 66 is low and since furthermore the output of indicator 32 is low the output of gate is low. This means that both inputs on gate 64 are low and therefore its output 39 high. As a result of this the mast 112 is driven towards its lower limit position 114. When the arm 113 reaches the limit position 114 the output of indicator 31 becomes high. As a result of this output 37 of gate 63 becomes low through which the driving of the arm is interrupted. Since output 1 of flip-flop 17 is high this results furthermore therein that the output of gate 66 becomes high through which output 39 of gate 64 becomes low and the driving of the mast is interrupted. If the switch 90 is open the mast is instead returned to its lower limit position 114 when output 1 of flip-flop 14 is high. In order to reach the predetermined bottom surface 103 an extension of the drill-rod 108 may be necessary. When the drilling machine 107 is in its front position on the feed beam 106, the tongs of the drill guide 110 are squeezed together through which the drill-rod 108 is held. Furthermore the output of indica tor 33 becomes high through which gates 52 and 53 are closed so that no pulses from sensor 3 can pass. The drilling machine 107 is disconnected from the drill-rod 108 and returned to its backward position on the feed beam 106. One more rod section is connected to the drill-rod 108 after which the drilling machine 107 is connected to the drill-rod extended in this way. When the tongs of the drill guide 110 are separated the output of indicator 33 becomes low and the drilling work can proceed as described above.

When the bottom surface 103 is reached the value in the preset display of counter 14 becomes zero and output 44 therefore high. Through this output 1 of flip-flop 18 becomes high and its output low. Output 40 of gate 68 therefore becomes high through which the hammer device of the drilling machine 107 is shut off as described above. The lamp 41 is lit up and indicates that the hole has been finished.

During the drilling work it can become necessary to feed the drilling machine 107 backwards e.g. if the drill-rod 108 shows tendencies of getting stuck in the drill-hole. When the drilling machine is fed backwards the sensor 3 delivers pulses from output UP. These are supplied to input UP on counter 8 and input R on flipflop via gate 52. As a result of the first pulse output 1 of flip-flop 10 becomes low and its output 0 high. Gate 55 is closed. When the drilling machine 107 is fed forwards again the sensor 3 delivers pulses from output DOWN. .Since output 0 of flip-flop 10 is high the pulses pass gates 53 and 54 to input DOWN on counter 8. When the value in counter 8 becomes Zero again a pulse is obtained from output BORROW. As a result of .this pulse output 1 of flip-flop 10 becomes high and its output 0 low. Through this gate 54 is closed at the same time as gate 55 is opened. The pulses from sensor 3 are now supplied to counter 14 as described above.

If the photo detector 116 already is above the reference surface 102 when the contact device 35 is pushed or if the photo detector during the upwards movement for some reason does not come in contact with the reference surface 102 the mast is fed up to its upper limit position. When the mast comes to this position the out put of indicator 21 becomes high. As a result of this output 1 of flip-flop 27 becomes high through which output 38 of gate 60 becomes low and the upwards movement of mast 112 is stopped. Furthermore output 40 of gate 69 becomes high through which the hammer device of the drilling machine 107 is stopped and the lamp 42 lit up. Furthermore the output of gate 61 becomes low. Since the outputs on indicators 31 and 32 both are low the output of gate 65 is low. This means that both inputs on gate 54 are low and therefore its output 39 high. As a result of this the mast 112 is fed downwards. When the photo detector 116 during the downwards movement of the mast comes in contact with the reference surface 102 the output of indicator 30 becomes high. Since the arm 113 already is in contact with the ground the output of indicator 19 is high. The output of gate 22 therefore becomes high through which output 1 of flip-flop 15 becomes high. Furthermore output 1 of flip-flop 27 becomes low through which output 40 of gate 68 becomes low and the lamp 42 turned off. The hammer device of the drilling machine 107 is restarted. Since the outputs 1 on flip-flops 17 and 27 both are low the output of gate 58 is low. Furthermore output 1 of flip-flop 20 is low so that the output of gate 61 is high. This means that output 39 of gate 64 is low and the movement of mast 112 is stopped. The system after this works as described above.

In the embodiment according to FIG. 4 a control system is used which differs from the one shown in FIG. 3 mainly thereby that the UP/DOWN counters have been excluded.

As in the system according to FIG. 3 a photo detector 116, an amplifier and filter 140, and an output device 141 which e.g. can be made as a Schmitt-trigger are used for sensing the reference surface 102. These three units correspond together to the indicator 30 in FIG. 3. The sensors 134, 135, and 136, which are connected to the feed motor 109, the motor of the arm 113, and the motor of the mast 112 respectively, are in this embodiment of a simpler construction than the corresponding sensors in the embodiment according to FIG. 3. They cannot sense the rotational direction of respective motors. Furthermore the monostable vibrators 137, 138, and 139 have been shown as separate units. Three indicators are used in the system according to FIG. 4, e.g. pressure sensors 131, 132, and 133 which substitute the indicator-provided tongs 33 in FIG. 3. These indicators indicate that the hammer device works, that the drillrod 108 rotates and that feed force is excerted respectively. The outputs of these indicators are all high at drilling.

When the switch 130 is moved to the position 127 gate 148 is supplied with voltage from conduit 71. Through this output 1 of flip-flop 143 becomes high. The mast 112 and the arm 113 are returned, via outputs 37 and 39, to the limit position 114. When this has occured the outputs of indicators 31 and 32 are high. When the switch 130 is moved to the position shown in FIG. 4 the monostable vibrator 28 delivers a logic 1- pulse from output 1. This pulse restores, via the draw magneto the counter 14. If the preset display of counter 14 before this showed zero the pulse passes gate 67 to counter 12. As a result of the pulse output 1 of flip-flop 18 furthermore becomes low output 1 of flip-flop 142 high and its output 0 low, and output 1 of flip-flop 143 low. Since the mast 112 is not in its upper position the output of indicator 21 is low. Both inputs on gate 68 are therefore low so that the valve 47 opens the pressure-fluid supply to the hammer device of the drilling machine 107. Since output 36 is high the arm 113 is driven towards the ground. Since the photo detector 116 is not in contact with the reference surface 102 the output of the output device 141 is low. The output 38 is high and the mast is fed upwards. The movement of the mast 112 and the arm 113 are registered via the sensors 136 and 135, the monostable vibrators 139 and 138, gates 149 and 150, adder 4, gate 152 and adder 6 in counter 14. The forward feeding of drilling machine 107 along the feed beam 106 is registered during drilling via the sensor 134, the monstable vibrator 137 and, since the outputs of indicators 131, 132, and 133 are high, the gate 151 in counter 13. These pulses are also supplied to the multiplier 11 where the number of them is modified by the value cos v which is obtained from the sensor 26. The pulses leaving multiplier 11 are supplied to counter 14 via adder 6. When the arm 113 reaches the ground the output of indicator 19 becomes high and gate 150 blocks signals from sensor 135. It is in this case supposed that the motor of arm 113 is provided with a mechanical clutch device which interrupts the driving of the arm when it hits the ground. When the photo detector 116 comes in contact with the reference surface 102 the output of the output device 141 becomes high. Through this output 1 of flip-flop 142 becomes low and its output high and output 1 of flip-flop 143 high. As a result of this,

the mast and the arm are returned to the limit position 114. Gate 152 is thereby closed. When the preset display of counter 14 becomes zero output 44 becomes high, through which output 1 of flip-flop 18 becomes high. Output 40 of gate 68 becomes high through which the hammer device of the drilling machine 107 is stopped by the valve 47. Furthermore the lamp 41 is lit up to indicate that the hole has been finished. Since the feeding of the drilling machine 107 along the feed beam 106 is registered only when the outputs of the indicators 131, 132, and 133 are high the drill-rod 108 can be extended also in this embodiment.

In the embodiment according to FIG. the mast 122 is mounted on the feed beam 106. A circuit 144 is provided in this system for generating a number of pulses which corresponds to the distance K in FIG. 2. This circuit replaces the arm 113 in FIGS. 3 and 4. The multiplier 11 has in FIG. 5 been moved so that the total number of pulses from sensors 134 and 136 are multiplied by cos v in accordence with the relation A (H K D) cos v obtained from FIG. 2 and the gate 153 has replaced gates 149 and 152 in FIG. 4. Otherwise the system according to FIG. 5 works in principle in the same way as the system according to FIG. 4 so that a detailed description of its function is unnecessary.

The above described and in the drawings shown embodiments of the invention are only to be regarded as examples which may be modified within the scope of the subsequent claims.

What I claim is: 1. A method of rock-drilling and/or earth boring of a number of drill-holes to an imagined predetermined and preferably plane bottom surface comprising:

generating a reference surface, defined by electromagnetic radiation, parallel to said bottom surface,

measuring the distance between said reference surface and the point at which drilling is to be initiated in a direction common to all holes,

adding the component, in said direction, of the depth of the drill-hole to the distance measured in said manner, and

interrupting drilling when the sum indicates that the bottom surface has been reached.

2. A device for rock-drilling and/or earth boring of a number of drill-holes to an imagined and preferably plane bottom surface comprising:

a drilling machine drivable along a feed device to drill holes to the bottom surface,

a registering device connected to the feed device to register the forward feed of the drilling machine along the feed device,

a device for generating a reference surface, defined by electromagnetic radiation, parallel to said bottom surface, and

means associated with the registering device for registering the sum of the distance in a predetermined direction between said reference surface and the point at which drilling is to be initiated and the component in said direction of the depth of the drill-hole.

3. A device according to claim 2 in which the registering device is arranged to register backward feeding of the drilling machine through which the position of the front end of a drill-rod associated with the drilling machine always is indicated.

4. A device according to claim 2 in which the registering device includes means through which registering of the feeding of the drilling machine can be disconnected when the drill-rod is extended.

5. A device according to claim 3 in which the registering device includes means through which registering of the feeding of the drilling machine can be disconnected when the drill-rod is extended.

6. A device according to claim 2 in which the registering device comprises means for presetting a value proportional to the distance between the reference surface and the bottom surface and is arranged for delivering a signal when drilling reaches the depth, relative to the reference surface, corresponding to the preset value.

7. A device according to claim 3 in which the registering device comprises means for presetting a value proportional to the distance between the reference surface and the bottom surface and is arranged for delivering a signal when drilling reaches the depth, relative to the reference surface, corresponding to the preset value.

8. A device according to claim 4 in which the registering device comprises means for presetting a value proportional to the distance between the reference surface and the bottom surface and is arranged for delivering a signal when drilling reaches the depth, relative to the reference surface, corresponding to the preset value.

9. A device according to claim 5 in which the registering device comprises means for presetting a value proportional to the distance between the reference surface and the bottom surface and is arranged for delivering a signal when drilling reaches the depth, relative to the reference surface, corresponding to the preset value. A

10. A device according to claim 6 comprising a power supply disconnector associated with the drilling machine and coupled to the registering device for disconnecting the power supply responsive to the delivery of said signal from the registering device.

11. A device according to claim 10 in which the device for generating the reference surface comprises a laser.

12. A device according to claim 11 in which a device for measuring the distance, in a predetermined direction, between the reference surface and the point at which drilling is initiated comprises a drivable mast provided with a photosensitive element for sensing the reference surface.

13. A device according to claim 12 in which the mast is a telescopic mast. 

1. A method of rock-drilling and/or earth boring of a number of drill-holes to an imagined predetermined and preferably plane bottom surface comprising: generating a reference surface, defined by electromagnetic radiation, parallel to said bottom surface, measuring the distance between said reference surface and the point at which drilling is to be initiated in a direction common to all holes, adding the component, in said direction, of the depth of the drill-hole to the distance measured in said manner, and interrupting drilling when the sum indicates that the bottom surface has been reached.
 2. A device for rock-drilling and/or earth boring of a number of drill-holes to an imagined and preferably plane bottom surface comprising: a drilling machine drivable along a feed device to drill holes to the bottom surface, a registering device connected to the feed device to register the forward feed of the drilling machine along the feed device, a device for generating a reference surface, defined by electromagnetic radiation, parallel to said bottom surface, and means associated with the registering device for registering the sum of the distance in a predetermined direction between said reference surface and the point at which drilling is to be initiated and the component in said direction of the depth of the drill-hole.
 3. A device according to claim 2 in which the registering device is arranged to register backward feeding of the drilling machine through which the position of the front end of a drill-rod associated with the drilling machine always is indicated.
 4. A device according to claim 2 in which the registering device includes means through which registering of the feeding of the drilling machine can be disconnected when the drill-rod is extended.
 5. A device according to claim 3 in which the registering device includes means through which registering of the feeding of the drilling machine can be disconnected when the drill-rod is extended.
 6. A device according to claim 2 in which the registering device comprises means for presetting a value proportional to the distance between the reference surface and the bottom surface and is arranged for delivering a signal when drilling reaches the depth, relative to the reference surface, corresponding to the preset value.
 7. A device according to claim 3 in which the registering device comprises means for presetting a value proportional to the distance between the reference surface and the bottom surface and is arranged for delivering a signal when drilling reaches the depth, relative to the reference surface, corresponding to the preset value.
 8. A device according to claim 4 in which the registering device comprises means for presetting a value proportional to the distance between the reference surface and the bottom surface and is arranged for delivering a signal when drilling reaches the depth, relative to the reference surface, corresponding to the preset value.
 9. A device according to claim 5 in which the registering device comprises means for presetting a value proportional to the distance between the reference surface and the bottom surface and is arranged for delivering a signal when drilling reaches the depth, relative to the reference surface, corresponding to the preset value.
 10. A device according to claim 6 comprising a power supply disconnector associated with the drilling machine and coupled to the registering device for disconnecting the power supply responsive to the delivery of said signal from the registering device.
 11. A device according to claim 10 in which the device for generating the reference surface comprises a laser.
 12. A device according tO claim 11 in which a device for measuring the distance, in a predetermined direction, between the reference surface and the point at which drilling is initiated comprises a drivable mast provided with a photosensitive element for sensing the reference surface.
 13. A device according to claim 12 in which the mast is a telescopic mast. 